This application claims the priority of German Application No. 198 03 386.9, filed Jan. 29, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a system for monitoring the inflation pressure of a vehicle tire having a device for detecting at least the vertical acceleration of the tire or of a vehicle component connected with the tire and the vehicle longitudinal speed, and an analyzing device which determines the tire inflation pressure from the measured vertical acceleration data and the measured vehicle longitudinal speed data. By means of systems of this type, it is possible to continuously monitor the tire inflation pressure,--in the following, also simply called "tire pressure"--also when the vehicle is driving. This makes it possible to detect excessive pressure drops in time.
It is known to derive the pressure of vehicle tires indirectly from rotational wheel speed measurements, which frequently are required anyhow; for example, for an anti-lock system and/or a wheel slip control system. As disclosed, for example, in German Published Patent Applications DE 44 09 816 A1 and DE 196 19 393 A1 as well as U.S. Pat. No. 5,513,523, these systems indirectly monitor the tire pressure normally using comparative operations between rotational wheel speeds of different vehicle wheels. They therefore usually permit only the detection of the pressure drop of one tire relative to other tires, but not an absolute determination of the tire pressure value.
From U.S. Pat. No. 5,285,523, the use of several parallel neuronal (or "neural") networks with different characteristics is known in a system for detecting the driving condition of a vehicle, in which case particularly the type of driven road, that is, an autobahn or a city road, etc., and the traffic situation, are to be determined while taking into account the detected driver behavior.
German Published Patent Application DE 43 40 746 A1 discloses a diagnostic system which, among other things, also permits a monitoring of the pressure of vehicle tires. In the process, the system uses a non-trainable estimating unit in the form of a so-called condition observer, in which case the dynamic system consisting of a wheel suspension and of a wheel is described by a pertaining condition differential equation system, on which the condition observer or the condition estimator is based.
From German Patent Document DE 29 05 931 C3, it is known to monitor the pressure of a vehicle tire indirectly based on detecting the vertical acceleration of the tire or of a vehicle part connected therewith. Specifically, by means of this known system, individual spectral fractions of the detected vertical acceleration information are analyzed for the monitoring of the tire pressure. For this purpose, the system contains per vehicle wheel, either an acceleration sensor and two parallel analyzing circuits which analyze different frequency ranges or a first acceleration sensor on a supporting component of each wheel and a second acceleration sensor at a point on the vehicle body situated close to the wheel as well as one analyzing circuit respectively which is connected behind the acceleration sensors and has a band pass frequency filter. The respective frequency filters are in both cases followed by a rectifier and an integrator. A comparison unit connected behind the analyzing circuit compares the analyzing information of a respective analyzing circuit with that of another analyzing circuit or with predetermined threshold values in order to monitor the tire pressure and the shock absorbers for each wheel.
German Published Patent Application DE 39 37 403 A1 furnishes the general teaching of detecting vibrations on the wheel carriers of a vehicle wheel at least in the vertical and in the longitudinal direction. This system uses the thus obtained vibration information, for example, for monitoring the tire inflation pressure. This known system is adaptively designed such that it learns the natural frequency of each wheel suspension over an extended period of time.
European Published Patent Application EP 0 455 993 A2 discloses a system for determining and/or monitoring the condition of a technical component of a motor vehicle, such as the tires, with respect to the tire pressure. Vibrations introduced into the chassis of the vehicle are measured on components of the wheel suspension relative to the vehicle body. In this case, values of the particularly stochastically excited vibrations of components of different wheel suspensions coupled with the technical component are measured and are processed to form characteristic values which are compared with assigned characteristic values previously determined in the same manner while determining deviations in a predetermined vehicle-specific frequency range. In this known system, the detection of the tire pressure comprises the measurement of the vertical accelerations on at least one wheel of the front axle and one wheel of the rear axle. From these measurements, a transmission function is determined which is relevant for the tire pressure determination and which formally links the forward wheel axle with the rearward wheel axle, which is physically implemented in a complex form by way of the vehicle body.
From European Published Patent Application EP 0 729 855 A1, it is known to use a previously trained neuronal network for determining the inflation pressure. The training takes place by means of example data with different tire inflation pressure values and vehicle condition values, such as vehicle longitudinal speed values, acceleration values and braking values, as well as straight ahead drive and cornering values. In a subsequent operating phase, the tire pressure is determined from the corresponding measured input quantities by the trained network.
The invention is based on the technical problem of providing a system of the above-mentioned type by which the vehicle tire inflation pressure can be determined at relatively low expenditures and with a comparatively high precision and stability. As required, the tire pressure is determined individually and separately for each vehicle wheel without the necessity of taking into account measurements on other vehicle wheels.
The invention solves this problem by providing a system having a device for detecting at least the vertical acceleration of the tire or of a vehicle component connected with the tire and the vehicle longitudinal speed, and an analyzing device which determines the tire inflation pressure from the measured vertical acceleration data and the measured vehicle longitudinal speed data. The analyzing device comprises a trainable estimating unit, particularly a neuronal network, which is trained by means of predeterminable training example data with various tire inflation pressure values and vehicle longitudinal speed values. In the trained condition, the analyzing unit determines the tire inflation pressure at least as a function of the measured vertical acceleration data and measured vehicle longitudinal speed data fed on the input side directly or in preprocessed form. For monitoring the tire inflation pressure by means of this system, the measured values of the vertical acceleration of the tire or of a vehicle component connected therewith, as well as of the vehicle longitudinal speed--in the following, also simply called "vehicle speed"--, will be sufficient. By using the trainable estimating unit, the system provides tire inflation pressure monitoring having a high precision and stability, in which case the absolute tire inflation pressure can be determined for each wheel individually. Furthermore, the system has one or several additional components, as described in the following.
As a first component, a device is provided for generating road condition information as a function of measured vertical acceleration data and of the measured vehicle longitudinal speed data, by which the activation and the deactivation of the estimating unit is controlled as a function of whether the momentary vertical acceleration and vehicle longitudinal speed are in each case inside or outside pertaining predeterminable value ranges. As a result, the active operation of the estimating unit can be limited to those situations which are in the range for which the estimating unit had previously been trained.
As a second component, devices for suppressing those estimated values of the estimating unit which result from situations outside the range for which the estimating unit was trained are connected behind the estimating unit.
As a third component, the vertical acceleration information is subjected to a preprocessing by means of a pertaining device which contains at least one analog-digital converter unit and a system condition determination unit connected behind. The latter computes one or several time derivatives of the measured vertical acceleration and supplies this information, in addition to the measured vertical acceleration itself, to the estimating unit as input quantities.
As an alternative to this derivation unit, a preprocessing unit provided as a fourth component contains an FFT unit behind an analog-digital converter unit, for carrying out a Fast Fourier Transformation, and a selection unit connected behind it by which those spectral fractions can be selected from the output signal of the FFT unit which contain the significant information concerning the tire inflation pressure.
As a fifth component, a data memory and an evaluating and optimizing stage are provided. The data memory is used instead of the estimating device in a training example data recording phase and in this recording phase stores the received training example data. In a training phase following the recording phase, the data memory and the evaluating and optimizing stage are connected behind the estimating unit in order to train it by means of the training example data furnished to it by the data memory.
In a system further developed according to the invention, the preprocessing unit contains an anti-aliasing filter which is connected in front of the analog-digital converter unit and prevents scanning errors of the analog-digital converter unit.
In a system further developed according to the invention, the preprocessing unit contains a digital low-pass smoothing filter which follows the analog-digital converter unit and which has a high-pass offset filter which follows it. As a result of the signal smoothing caused by the low-pass smoothing filter, a clearly lower scanning rate can be used in the high-pass offset filter. In addition, the high-pass offset filter compensates for any drift of the conventional vertical acceleration sensors which is in a minute range.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.